Classifications

• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T5/00—Image enhancement or restoration
  • G06T5/90—Dynamic range modification of images or parts thereof
  • G06T5/94—Dynamic range modification of images or parts thereof based on local image properties, e.g. for local contrast enhancement
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T5/00—Image enhancement or restoration
  • G06T5/40—Image enhancement or restoration using histogram techniques
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
  • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
  • H04N21/40—Client devices specifically adapted for the reception of or interaction with content, e.g. set-top-box [STB]; Operations thereof
  • H04N21/43—Processing of content or additional data, e.g. demultiplexing additional data from a digital video stream; Elementary client operations, e.g. monitoring of home network or synchronising decoder's clock; Client middleware
  • H04N21/431—Generation of visual interfaces for content selection or interaction; Content or additional data rendering
  • H04N21/4318—Generation of visual interfaces for content selection or interaction; Content or additional data rendering by altering the content in the rendering process, e.g. blanking, blurring or masking an image region
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
  • H04N21/40—Client devices specifically adapted for the reception of or interaction with content, e.g. set-top-box [STB]; Operations thereof
  • H04N21/43—Processing of content or additional data, e.g. demultiplexing additional data from a digital video stream; Elementary client operations, e.g. monitoring of home network or synchronising decoder's clock; Client middleware
  • H04N21/44—Processing of video elementary streams, e.g. splicing a video clip retrieved from local storage with an incoming video stream or rendering scenes according to encoded video stream scene graphs
  • H04N21/44008—Processing of video elementary streams, e.g. splicing a video clip retrieved from local storage with an incoming video stream or rendering scenes according to encoded video stream scene graphs involving operations for analysing video streams, e.g. detecting features or characteristics in the video stream
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N5/00—Details of television systems
  • H04N5/44—Receiver circuitry for the reception of television signals according to analogue transmission standards
  • H04N5/57—Control of contrast or brightness
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T2207/00—Indexing scheme for image analysis or image enhancement
  • G06T2207/10—Image acquisition modality
  • G06T2207/10024—Color image
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2360/00—Aspects of the architecture of display systems
  • G09G2360/16—Calculation or use of calculated indices related to luminance levels in display data

Definitions

• the invention relates to a method of setting contrast in digital image processing in which a brightness distribution in the form of a histogram is produced from image pixels and the histogram is revised with the help of transfer functions, and to an arrangement of suitable design.
• a digital image picked up in a known fashion is composed of individual picture elements or pixels, with each pixel having assigned to it both a brightness, or what is referred to as a gray shade, and also, in the case of a colored digital image, a tristimulus value, i.e. a color.
• An image picked up in this way may either be stored immediately in a suitable storage medium or may be reproduced on any desired display device such as, for example, an LCD screen.
• the display device may have only a limited so-called dynamic range, i.e. that the maximum brightness or gray shade that is able to be reproduced by the display device at a pixel usually differs to only a limited degree from the minimum gray shade or brightness that can be shown. If however the image that is shown on such a display device is one that has been picked up digitally and that contains wide differences in contrast, such as, for example, a shot of a person or an object taken against light coming from behind the person or object in which there are extreme contrasts between light and dark, then the differences in brightness concerned cannot be exactly reproduced on the display device. This applies both to the reproduction of single images and to the reproduction of a sequence of images picked up digitally in the form of a video image.
• the histogram or rather the values which have been read into it, to be revised, in order in particular to adapt the maximum differences in contrast in the histogram to the capabilities of the display device. This is done for example by applying to the input signal a non-linear color-code assigning function by which given intervals in the brightness distribution are made larger and others are made smaller in order to correct the histogram.
• US 2005/0035974 Al also describes a histogram that is known per se and such as is used in electronic image processing.
• the mathematical revision of the histogram is performed with the help of a fixed number of transfer functions, which number remains constant in the course of the adaptation process.
• the transfer functions are decided on before the histogram is revised, which means that adaptation to different image contents is not possible.
• An appropriate arrangement for this purpose is also to be provided.
• the key concept underlying the invention is that a linear increase in contrast between the individual pixels or picture elements is made in only one region of the image, i.e. in only a section of the entire area that is shot.
• the gray values and/or the tristimulus values are acquired in the histogram and are corrected linearly in the appropriate way, in such a way that the correction corresponds to the maximum resolution in contrast that is possible on the associated display device.
• What is achieved in this way is that, in the section or region that is selected of the digital shot, use is made of the maximum contrast available, and in this way the reproduction of the maximum possible information becomes possible on, for example, an LCD display.
• the pixels belonging to the region selected that have the lowest and highest brightness value are detected, and all the pixels' values lying therebetween are adapted linearly in the appropriate way in order to assign the minimum brightness able to be shown by the display device to the lowest brightness value and the maximum brightness able to be shown by it to the highest brightness value.
• the region that is revised linearly in this way either to be laid down by a user himself, in the case for example of digital image processing on screen, or for the region having the greatest density of information to be selected automatically. Fuzzy logic processes may also be used for this purpose in a known fashion.
• This may, in particular, be done by collecting a brightness distribution for the image, distributed in a fuzzy manner, in a histogram, in order in this way to obtain an assignment of the brightness and/or tristimulus values to the image. From this assignment function, the region having the highest density of information can then be determined automatically by assuming that a large change in the tristimulus or brightness values in a small space represents a high density of information.
• the terms "histogram” or "filtered histogram” in what follows is not a histogram as understood in the prior art described above as the filtering processes according to the invention not only assigns the measured data to fixed classes but also classifies it into different classes with the help of a fuzzy assigning function.
• the advantage of the invention lies in the fact that an automatic adaptation is performed of any desired images to the capabilities of the display device, because the differences in contrast that are produced are always only ones that the display device is actually able to show with sufficiently good quality. Also, the method calls for a substantially lower computing capacity. It goes without saying that the method steps described above may be implemented in an appropriate arrangement by either hardware and/or software means and may for example be incorporated in the form of a microprocessor in a digital camera.
• the transfer function with which the histogram is revised in a manner known per se is, as claimed in claims 3 and 7, preferably not laid down or preset prior to the image processing proper but is only determined from the histogram.
• the region that contains the highest density of information, and whose contrast is to be increased linearly in what follows is first determined from the digital image.
• that transfer function is selected with which the best adaptation will be possible to the capabilities of the display device. This can be done automatically in an arrangement of suitable design, by for example simulation using different transfer functions.
• Fig. 1 shows a schematic block diagram of the method
• Fig. 2 shows a prefiltered histogram
• Fig. 3 shows the distribution of the data
• Fig. 4 shows the clipping.
• FIG. 1 From the schematic block diagram in Fig. 1 can be seen the basic procedure followed in the image processing, with data interfaces being shown as oval boxes and processing operations by data processing devices being shown as rectangular boxes.
• the processing of the pixels takes place in real time during the flow of data which arrives as a data stream representing a video image. What are used for the processing are a histogram unit for analyzing the scene shown and a pixel control unit for the assignment of color. Algorithmic calculations have to be performed for each pixel. In contrast to this, the processing of the parameters ideally takes place only during the vertical blanking. An assignment function for the red, green and blue (RGB) color codes for the next data block or field is to be defined in this case by using the statistics of the previous one. The period covered by the process may also be extended to the next active data-processing block or even longer, so long as the result is available in sufficiently good time to obtain temporal coherence between the block of transmitted data that is analyzed and the one that is corrected.
• RGB red, green and blue
• the algorithmic calculations are to be performed only once per block or field of transmitted data. This allows successive treatment by hardware and/or software means.
• the segmentation unit establishes the region of the color codes that covers the major part of the complete color distribution, and determines a reasonable target range, to which said major part is assigned for the purpose of improving contrast.
• the result is processed using a set of two reference points in the color space for the assigning function and is passed through a filter.
• An interpolation unit lays down the clipping characteristics at the top and bottom ends of the transfer or assigning function and converts these characteristics into coefficients for the color assignment. These values are brought up to the latest state at the beginning of an active block of transmitted data. The minimum delay in the correction is therefore a single block or field of transmitted data.
• the invention may also be applied to a system having a buffer store, with the analysis and change of the color distribution taking place in the same block of transmitted data. In this way the processing of the pixels is able to be performed in a more flexible way when the implementation is wholly or partly by software means.
• PIXBITS is the number of bits, usually eight or ten, which is used for the coding of a single color channel.
• BINBITS is the number of most significant color code bits that are used for the addressing of a histogram counter. A suitable value that will be used in what follows is two. This value controls the width of the pre-filter and the size of the histogram data interface. The actual number of cell counters n cnt works out as:
• f 1)O may, in addition, be weighted in accordance with the proportional brightness of the associated component. This is of greater importance for the green channel than for the blue one.
• the division determines a range of color codes that is focused on the maximum of the color distribution cntj and that assists with the increase in contrast. It is defined by two statistical parameters segin 0)1 that, as can be seen in Fig. 3, specify the normalized weight of distribution to the left of the region boundary rcirny :
• the center region has a linear increasing factor applied to it to increase contrast, whereas the outer regions are compressed using a soft-clipping algorithm that is used in the downstream interpolation unit.
• the setting of the minimum for dcout to zero stops the center region from being compressed and the outer regions from being too heavily boosted if color distributions are being processed that are concentrated on dark and/or light colors.
• the interpolation unit generates polynomial coefficients that form an assigning function that extends through the two reference points, that assigns these two points to one another linearly, with which parametrizable clipping is possible in the outer regions and with which no gaps or discontinuities occur even when the accuracy of calculation is low.
• PC 1 (couto - COUt 1 ) / (CUi 1 - cin 0 )
• the behavior of the outer regions can be controlled by a set of statistical parameters.
• boundary conditions will be elucidated by way of example. The following conditions are common to all the following methods of interpolation:
• a linear soft clip may be applied, of the kind that is shown in Fig. 4 by curve E, in which pc2 0) 2 is set as equal to zero.
• curve E in which pc2 0) 2 is set as equal to zero.
• the clipping behavior may preferably be implemented by slight changes in the assigning function at cin with, at the same time, the clipping in the outer regions being sharp.
• What is used for this purpose is a set of statistical parameters ipolclip 0)1 that limit the gradient for the transfer function to c m in,m a ⁇ - In what follows it will be merely the upper region that is elucidated, the lower region being calculated in a corresponding way.
• a change in contrast set by the user is also possible. Particularly when there is back-lighting, as in LCD television sets for example, this back-lighting can be acted on dynamically with the invention. When dark images are being shown on the screen the back-lighting is reduced and at the same time the contrast of the darker shades of color is increased and the lighter shades of color are compressed. In simple terms, what this means is that to a viewer a black appears even blacker whereas a shade of gray remains unchanged and a light or white shade of color is dimmed.

Landscapes

• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Theoretical Computer Science (AREA)
• Computer Hardware Design (AREA)
• Facsimile Image Signal Circuits (AREA)
• Image Processing (AREA)
• Apparatus For Radiation Diagnosis (AREA)
• Picture Signal Circuits (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (2)

Family

ID=37704324

Family Applications (1)

Country Status (5)

Cited By (1)

Families Citing this family (3)

Citations (2)

Family Cites Families (3)

• 2006
  • 2006-07-31 JP JP2008525675A patent/JP2009505469A/ja active Pending
  • 2006-07-31 CN CN200680028713.2A patent/CN101248455A/zh active Pending
  • 2006-07-31 WO PCT/IB2006/052606 patent/WO2007017785A2/en active Application Filing
  • 2006-07-31 US US12/063,060 patent/US20100195905A1/en not_active Abandoned
  • 2006-07-31 EP EP06780247A patent/EP1915736A2/en not_active Withdrawn

Patent Citations (2)

Also Published As

Similar Documents

Legal Events